Our team gets a lot of questions about the blacklisting of shared pools of IP addresses. While we are constantly working to keep our IP pools clear of any and all blacklists, there will be times when an address pool does land on a blacklist. Here’s what you should know about blacklists, and how they might affect shared and dedicated IP addresses.

There are literally thousands of blacklists for thousands of reasons— most of which do not affect the average sender. Most large ISPs have their own internal blacklists and scoring systems. The primary independent blacklist in use today is Spamhaus.

We monitor blacklists and immediately work to resolve any blacklisting that affects our customers. We also monitor our IP pools and terminate or suspend and educate any sender found to have caused a blacklisting. This is in order to ensure that the blacklisting is delisted at the earliest opportunity.

Causes of Blacklisted IP Addresses (And What to Do About Them)

Many blacklists are temporary and resolve themselves while not without providing an option for early delisting. If you have a recipient domain returning a bounce citing with a blacklist (called out or even just the word blacklist in the bounce response), first check to see if 100% of that domain is blocked. If not, it may be a temporary block or even a personal blacklist created by the subscriber themselves. In either case, no action is necessary.

Mailing to spam traps is the single most common cause for blacklisted IP addresses. Therefore, if you want to ensure your messages are delivered and delivered to the inbox, you should avoid hitting spam traps. You can do this by following best practices and sending to only directly opted in subscribers that are actively engaged with your mail stream. In addition, periodically removing unengaged subscribers will help to avoid spam traps.

A good rule of thumb is that actively engaged subscribers will open and/or click on your daily messages at least once in a 30 day time frame and at least once on your weekly messages within 90 days. Therefore, you should adjust sending frequency to subscribers that are not actively engaging with your mail stream.

After six to nine months of no engagement, you can run a re-engagement or win-back campaign. From there, you should permanently remove any recipients that don’t engage with your mail after a maximum of three attempts. Ultimately any subscriber that has not opened or clicked on your messages in the past ten months should be permanently removed from your list as they run the risk of becoming a spam trap.

It also is imperative that you migrate your suppression list from your previous email provider. This ensures that you don’t re-enable an inactive subscriber’s email address that has been recycled into a spam trap.

You should also make sure that your sign-up page and forums have anti-abuse measures in place such as captcha or link verification. A good way to avoid typos is to simply require that subscribers type their email address into your form twice. This is all to avoid high rates of complaints, unknown email addresses, spam traps and low read rates. All of these factors cause poor delivery and high spam filtering, which affect everyone else sending and following best practices in your shared environment.

Blacklists on Shared IP Pools

SparkPost’s deliverability team monitors and requests delisting when possible for any blacklist on our shared IP pools. However, we know that many minor blacklists do not affect our users, and we prioritize our efforts accordingly. If you look up your shared IP, it’s possible you might see blacklistings. However, you can rest assured that either a resolution is in progress or they do not affect our users.

However, if you do have a blacklist that shows up in your bounce logs causing a bounce rate above 1%, please open a support case with the following information so we may investigate. Here’s how:

Bounce log with name of blacklist called out in it. If the block doesn’t have the name of the blacklisting, it’s likely an internal temporary blacklist for that ISP. However, feel free to send the bounce log with the domain included.

Email address you were attempting to mail to.

Your sending domain.

Number of subscribers affected per total number of subscribers mailed. (ie #blocked/#sent)

Date and time of occurrence.

Blacklists on Dedicated IPs

If you have a dedicated IP, but you haven’t subscribed to SparkPost’s Premium add-on plan (which offers dedicated technical account management and deliverability support), you will need to monitor and request delisting for your own blacklistings.

When you see a bounce calling out a blacklist, and the bounce rate is above 5%, you should first investigate and remove any subscriber that has not opened or clicked on your message in the past three months. Then, follow the link in the bounce message to request delisting. It is best to inform them of what actions you have taken as well as request information about the cause, so that you can investigate further when requesting delisting so that the blacklister will understand that you are serious about following best practices.

Finally, if you want to truly separate your sending reputation, remember to set up a custom bounce domain. In addition, you can setup custom click tracking (if you use our click tracking).

-Tonya

PS: Other questions on blacklisted IP addresses or deliverability topics? Leave them below, find us on Twitter or post them in our community slack.